Process for manufacturing selenium cells



Aug. 28, 1951 D. A. DRIVER PROCESS FOR MANUFACTURING SELENIUM CELLS 7Original Filed llay 30, 1945' Patented Aug. 28, 1951 PROCESS FORMANUFACTURING SELENIUM CELLS Douglas Louis Ashton Driver, London,England,

assignor, by mesne assignments, to International Standard ElectricCorporation, New York, N. Y., a corporation of Delaware Originalapplication May 30, 1945, Serial No.

Divided and this application October 28, 1947, Serial No. 783,341; InGreat Britain May 5, 1944 7 Claims. (Cl. 175-366) I The inventionrelates generally to an improved method for the manufacture of seleniumcells such as dry rectifiers and photocells and in a more particularsense it is concerned with articles, useful in making such cells whereinthe selenium is utilized in a new form.

When selenium is employed in the manufacture of electric rectifiers orphoto-electric cells, it is usually applied to the metal base plates inthe form of powder which, after spreading over the plates is thensubjected to heat and pressure to form an adherent coating.

According to the present invention the selenium is utilized in the formof a felted or matted mass of filaments or fibres resembling, inappearance, glass wool. This selenium felt or mat may be manufactured incontinuous sheets or strips of any desired thickness and discs or othersuitable shaped pieces may be out therefrom. These pieces may be made inthe proper size to be pressed directly on the base plates to form thedesired coated plates which are subsequently processed and completedaccording to any of the well known methods used in the manufacture ofrectifiers or photo-electric cells.

The selenium felt or wool may be produced by spraying molten seleniumfrom one or more nozzles by air or gas under pressure. The seleniumforms into fibers immediately on extrusion from the nozzles, and thefibres mat together to form a loosely felted wool-like mass. As will beexplained in detail below, the spraying apparatus may be similar to thatused for flameless metal spraying. The spraying nozzles consist of anarrow inner pipe, the mouth of which is surrounded by an annular nozzleto which compressed air is supplied for ejecting the selenium, and thesupply of selenium to the inner pipe may be controlled by a needlevalve.

The invention will be explained with reference to the accompanyingdrawings in which:

Fig. 1 shows a perspective view of apparatus for producing selenium feltor wool according to the invention;

Fig. 2 shows a top view of part of a strip of selenium felt which hasbeen sprayed onto a metal plate;

Fig. 3 shows a transverse section of Fig. 2; and

Fig. 4 is an end elevation of a complete rectifier unit made inaccordance with the present invention.

A perspective view of an apparatus for producing the selenium felt isshown in Fig. l of the accompanying drawings.

The apparatus is mounted in an enclosure builtaround a rectangular frameI of angle-iron. The top and sides of the enclosure have been removed inorder to show the internal parts. Supported from the top of the frame ontransverse bars is the selenium sprayer 2 which comprises anelectrically heated hollow metal tank. Three or other suitable number ofspraying nozzles 3 (not visible in Fig. l) are fixed through the bottomof the sprayer tank. The selenium is heated in the tank to a temperatureabove 220 C. so as to maintain it in a molten condition, and is blownthrough the nozzles by compressed air supplied from pipes 4 each fedfrom a. main air pipe 5 which'passes through a heating box 6. The mainair supply is controlled by a reduction valve 1 and individual needlevalves 8 control the air supply to the pipes 4. A thermometer 9 andpressure gauge ID are provided for the main air supply. Individualneedle valves (not shown) are provided for the nozzles 3 to control thesupply of the melted selenium.

An endless band 29 is driven continuously in the direction of the arrowover rollers 3|], 3| and 32 by means of an electric motor 33. The driveincludes a variable. speed gear 34 by which the velocity of the band maybe adjusted. The horizontal portion of the band travels beneath thenozzles 3 of the sprayer 2. The selenium emerging from the nozzlessolidifies into fine fibres which consolidate upon the band and form aloosely matted felt like that shown in Figs. 2 and 3. The thickness ofthe felt depends on the number of nozzles, on the rate at which theselenium is sproyed, and on the velocity'of the band 26. A fixedhorizontal platform 35 placed close to the band 29 where it turns downover the edge of the edge of the roller 32 is employed to intercept thestrip of felt which is continuously formed, and to direct it out of theapparatus. An exhaust flue 36 is provided to remove undesirable fumesfrom the insideof the apparatus.

The spacing of the nozzles 3 and their distance from the band 29 shouldbe adjusted so that a selenium felt of even thickness is obtained.

The felt or wool manufactured in this manner may be stored in rolls ifdesired, and may be cut up into discs of the proper size and shape forpressing directly onto the metal base-plates in the manufacture ofrectifiers or photo-electric cells.

In accordance with this last modification of the invented process, themetal base-plates are fedfrom the left hand side onto the band 29 andare covered directly with the selenium felt as they pass under thenozzles 3, or a large piece of sheet metal is passed under the nozzleson the band (or by-other means) and is covered with a layer of felt ofsuitable thickness which is afterwards pressed. onto the sheet to formthe desired selenium coating. The covered metal sheet is then cut intodiscs of the desired size. Figs. 2 and 3 show such a metal sheet 31covered with a layer of felt '88 and supported on the travelling band29.

The pressing of the selenium felt onto the base plate takes place in apress at a suitable temperature for obtaining the selenium coating inthe desired form. the process being similar to that employed whenselenium is applied to the plates in the form of powder, except that thepressing time is different and generally shorter under otherwise similarconditions. The pressing may for example takes place attemperaturesbetween about 1 0 C. and 145 C. at pressures between about800 and 6000 pounds per sq. inch, the necessary pressing times varyingbetween about A and 5 minutes.

After coating the base plate in this manner the selenium may be furtherheat treated according to the usual practice in order to produce thedesired electrical semiconductor properties, and the counterelectrode isthen applied over the selenium coating, as shown in Fig. 4, wherein baseplate 31 is covered by a layer 38 of felted selenium with asuper-imposed counterelectrode ,alloy layer 39 forming the otherrectifier electrode. In the case of a photo-electric cell, thiscounterelectrode will, of course, be of transparent or translucent.

In the followin claims the term selenium cell means both a seleniumrectifier cell and a selenium photo-cell.

This-application is a. division of co-pending appilcation Serial Number596,697, filed May 30, 1945, entitled Manufacture of Selenium Products,now Patent No. 2,445,768, issued July 27, 1948.

I claim:

1. An article useful in the manufacture of selenium cells comprising ametallic base element bearing an adherent layer comprising hot pressedfelted selenium fibers.

2. An article useful in the manufacture of selenium cells comprising ametallic base element bearing an adherent layer comprising a felt formedof selenium fibers loosely matted together and hot pressed onto thebase.

3. In the manufacture of selenium cells of the type comprising a baseelement bearing-a layer of selenium, the improvement that comprisescoating a base plate with selenium by placing upon the plate a piece ofselenium felt and compressin the felt onto the plate at an elevatetemperature. 7

4. In the manufacture of selenium cellsof the type comprising a baseelement bearing a layer of selenium, the improvement that comprisescoating a, base plate with selenium by spraying molten selenium on tothe plate under air or gas pressure in such manner as to form thereonselenium felt of appropriate thickness. and compressing the felt ontothe plate at an elevated temperature.

. 5. The method according to claim 4 in which the compressing isperformed at a temperature below the melting point of selenium.

6. The method according to claim 4 in which the compressing is performedat a temperature between C. and 0., thepressure employed lying between800 and 6000 pounds per sq. inch.

7. The method of manufacturing a selenium cell which comprises the stepsof compressing a matted mass of selenium filaments onto a metalbase-plate to form a coating thereon, heat-treating the said seleniumcoating, and applying a counterelectrode to the said selenium coating.

DOUGLAS LOUIS ASHTON DRIVER.

REFERENCES CITED The following references are of record in the file ofthis patent? UNITED STATES PATENTS

4. IN THE MANUFACTURE OF SELENIUM CELLS OF THE TYPE COMPRISING OF A BASEELEMENT BEARING A LAYER OF SELENIUM, THE IMPROVEMENT THAT COMPRISESCOATING A BASE PLATE WITH SELENIUM BY SPRAYING MOLTEN SELENIUM ON TO THEPLATE UNDER AIR OR GAS PRESSURE IN SUCH MANNER AS TO FORM THEREONSELENIUM FELT OF APPROPIATE THICKNESS AND COMPRESSING THE FELT ONTO THEPLATE AT AN ELEVATED TEMPERATURE.